The Smalltalk project, which started at Xerox Parc, was created with the purpose of allowing children to be able to use computing systems. It aimed to create a personal computing environment, where a single user could have access and control over their computer, like drawing pictures, file handling, and text editing.
The smalltalk language is object-oriented, much like simula before it. It primarily works by passing messages from one object to another. Classes have instances which share common characteristics, such as how they respond to messages.
Operators are thought of as messages that might take one or more
arguments. For example, +4 as is would apply unary
+ to 4, leaving it as 4.
No part of a complex system should depend on the internal details of any other part. Objects should send messages to obtain results, and similar behavior should be grouped into classes. Factoring of the information structure and behavior is provided by subclassing.
All references in Smalltalk are to objects. They may be atomic, or
consist of several named fields, which refer to other objects. Smalltalk
does away with referencing memory addresses, such as getting the y
coordinate in a point in a Cartesian plane by
loading the second word relative to the point p. This would
break on polar coordinates, for example. The response to a message is
implemented by a method, which reads or writes a data field, or sends
further messages to achieve the desired response.
Classes can inherit from each other, in which case they inherit all the traits of their parent class.
All objects in smalltalk are active, so they can respond to messages at any time. The libraries used to implement the system is a set of useful superclasses from which classes can derive. For example, windows are inheritable from the system library. The window class also responds to behavior, such as clicks within the window, and transitioning from active to inactive.
Classes in smalltalk also respond to operator overloading, and have
setters and getters. They also allow themselves to be turned into a
string stream which can then be printed. As well, numbers can implement
the full set of relational operators by only defining <,
=, and >.